1. Field of the Invention
Aspects of the present invention relate to an organic light emitting diode (OLED) display device capable of minimizing a threshold voltage variation of a driving transistor in a pixel circuit, minimizing lowering of an aperture ratio, and minimizing power consumption by applying the same range of data voltages to respective pixels.
2. Description of the Related Art
Flat panel display devices, for example, liquid crystal display devices and organic light emitting diode (OLED) display devices, are lightweight and thin and are widely used as alternatives to cathode ray tube (CRT) display devices. Among these flat panel display devices, OLED display devices, in particular, have attracted considerable attention for their advantages of excellent brightness, wide viewing angle, and extra-thinness due to a back-light being unnecessary in comparison with LCD.
OLED display devices display images by forming excitons through the recombination of electrons and holes injected into an organic thin film from a cathode and an anode. The excitons generate a specific wavelength of light as the electrons and holes recombine.
OLED display devices are classified as a passive matrix type and an active matrix type depending upon the manner in which they are driven. The active matrix type has a circuit using a thin film transistor (TFT). Although the passive matrix type is easily manufactured as its display area is simply formed by an anode and a cathode in a matrix, the use of the passive matrix type is limited to small displays due to low resolution, a high driving voltage, low life-span of materials, etc. On the other hand, the active matrix type has a TFT in every pixel of a display area to apply a uniform current to each pixel, and thus may exhibit stable brightness. Also, the active matrix type plays an important role in realization of high resolution and large displays because of its low power consumption.
The OLED display devices have a specific variation in threshold voltage of a TFT in each pixel during a fabrication process of the TFT, which results in a non-uniform brightness of the OLED display device. Thus the OLED display devices generally have a pixel circuit including a compensation circuit to compensate for the threshold voltage variation. However, the OLED display device having such a compensation circuit requires several TFTs to form the compensation circuit, thereby requiring complicated pixel circuits which decrease a light emitting area due to a reduction in aperture ratio of each pixel.
Also, to realize full-color displays, the OLED display device includes several pixels, such as red, green, and blue pixels. However, since the respective pixels have different efficiencies in their own organic light emitting diodes, data signals with different voltages have to be applied to the respective pixels in order to obtain a uniform brightness from the respective pixels, and thus data driving units that apply the data signals have to be formed in each pixel. Also, a voltage range of the data signal is also increased, and thus the data driving unit is complicated and power consumption increases.